The present invention relates to bearings and, more particularly, to an active mechanical bearing for an axially rotatable member.
Mechanical bearings have been designed and used for many centuries to support shafts or other axially rotatable members. The design of a mechanical bearing typically makes the same quite reliable and rugged. Mechanical bearings are generally classified as journal, ball or roller bearings. Journal bearings are subclassified as standard journal, tilt pad and compliant.
A major problem with many mechanical bearings is that they are dirty in the sense that they often require an oil or other lubricant to be in contact with the rotating part. In this connection, many mechanical bearings are oil film bearings. That is, even though the mechanical bearing may have what is referred to as a bearing surface, the actual substance which is in contact with the rotatable member is an oil film which is formed between such bearing surface and the rotatable member. Another problem with most mechanical bearings is that they are passive, i.e., the amount and type of support such a bearing provides to a rotatable member cannot be controllably changed during the bearing function. That is, the support provided by such a bearing is fixed and cannot be changed in real time to take potential feedback or other information into consideration.
Non-contact bearings, such as magnetic bearings, are sometimes used because of these problems. A magnetic bearing provides the bearing function by suspending a rotating part relative to a supporting structure with a magnetic field. While magnetic bearings are conducive to feedback because the field, and, hence, the bearing support can be changed, a magnetic bearing design typically is quite expensive compared to the cost of a similar mechanical bearing. Moreover, magnetic bearings often require back-up with a conventional mechanical bearing to prevent a failure from having catastrophic results.